1. Field of the Invention
The present invention relates to an anti-pinch device for chain saws.
2. Prior Art
When using a chain saw to cut wood, such as trees, logs, etc., it is not uncommon to utilize several other tools, such as wedges of steel or plastic, pry bars, chains or log lifters to move the wood such that the chain saw blade does not become trapped or pinched within the saw cut. In some situations, tree cutters must utilize an additional saw to cut out a severely pinched chain saw. To reduce the incidence of pinching, a potentially dangerous technique, called "under bucking", is used wherein the tree cutter undercuts the log and uses the top portion of the chain saw bar or blade to cut the bottom of the log. In normal cutting practice (called "over bucking"), the bottom of the saw bar is used, the log is beneath the saw blade or bar, and the direction of chain rotation pulls the saw to the work (neutralizing any cutting forces) requiring the operator only to guide the saw. In the "under bucking" technique, the top of the bar is used, and the log is above the saw blade or bar such that the saw is thrust towards the operator due to the direction of chain rotation. Accordingly, the operator has to supply the cutting reaction force in addition to guiding the saw and maintaining his stance. It is apparent that the safety of the under bucking operation is clearly inferior to the conventional over bucking method.
Under bucking traditionally is used when it s judged that the work (e.g., a log) is positioned such that saw pinching will occur if over bucking is attempted. The design of the present invention makes it not only impossible to under buck the log (with the pinch arm in place) but also eliminates the need that arose from the envisioned potential pinching tendencies in the over bucking operation.
The practice of under bucking is extremely dangerous for several reasons. It places the operator in an unstable position, leaves the underside of the chain saw bar or blade exposed (which could be disastrous in the event of chain breakage) and further, with today's powerful, high speed saws, the saw may suddenly come free thereby increasing the possibility that the saw will rotate backwards toward the tree cutter or operator. Since the tree cutter is bringing the saw either vertically upward or horizontally away from the initial cut, control of the saw may be lost and the cutter's stability is at risk.
Some improvements are available in the art to improve the operation and/or safety of chain saws. Chain brakes, upper hand guards and saw bar or blade nose protectors are available and are primarily designed to minimize the injury due to kickback. These devices tend to impair or preclude some cutting procedures. For example, boring (cutting with the nose of the bar into a blind hole) is not possible with a bar nose protector installed. As a result, the nose protector is quite often removed and never reinstalled. Similar efforts are somtetimes undertaken to defeat other safety features that are perceived as unwieldy for whatever reasons.
U.S. Pat. No. 3,042,088 Filion et al discloses a kerf spreader that is attached to the housing of a chain saw. The kerf or saw cut is maintained at its original width at a single point due to the insertion of a tapered disc carried on an arm that extends longitudinally along a portion of the chain saw blade. The arm holding the kerf spreading disc is maintained in a housing such that the arm can move longitudinally with respect to the housing. The housing for the arm is rotatably attached to the chain saw motor mount.
U.S Pat. No. 3,636,996 to Lanz discloses a chain saw anti-pinch guard arm that is pivotally mounted to the chain saw housing and forms a lever, one end of which is attached to the chain saw blade. U.S. Pat. No. 4,294,012 to Lanz discloses a chain saw anti-pinch guard arm with a handle and an arm that is pivotally attached to the chain saw blade. U.S. Pat. No. 4,447,953 to Lombardino et al discloses a chain saw guard that is in a plane substantially perpendicular to the flat plane defined by the saw blade. U.S. Patent No. 4,335,513 to Owens discloses a safety bar for a chain saw that is pivotally mounted to a handle of the chain saw. U.S. Pat. No. 4,290,302 to Nadenoff discloses a chain saw guard that is relatively fixedly mounted above the chain saw blade in a plane substantially normal to the blade. U.S. Pat. No. 4,060,844 to Hampton discloses a chain saw safety bar that sits above the chain saw blade and is rotatably mounted to the chain saw housing. U.S. Pat. No. 3,808,684 to Ludwig discloses an attachment bar for a chain saw that consists principally of a sheath that covers almost all of the chain saw blade and is rotatably mounted on an aft region of the chain saw blade. U.S. Pat. No. 3,754,328 to Knerr discloses a guard for a chain saw that is also pivotally mounted to an aft region of the chain saw blade. U.S. Pat. No. 3,384,136 to Marin et al discloses a chain saw guard that is rotatably mounted to the chain saw housing.